According to Bohm, we should be asking questions in the fish shop: What type of fish is it? How was it caught? How long does it live?

This is the only way we can make environmentally informed decisions about the seafood we buy, he says.

Overseas, the demand for greener seafood is growing.

Major seafood retailers such as Tesco and Wal-Mart have committed to stocking their shelves exclusively with fish that was harvested or raised sustainably.

Yet in Australia, with several hundred species of seafood to choose from and little support from major retailers, making a green choice can be confounding.

Seafood sold in Australia must be labelled with its country of origin. "But what does that tell you?" asks Bohm.

"Whether a fish is from New Zealand or South Africa does not help you make a better choice environmentally."

To help us make real choices about the seafood we buy, the AMCS has published a Sustainable Seafood Guide. It recommends we say "no thanks" to gemfish and tuna, "think twice" before we tuck into prawns, and make a "better choice" by buying Western Australian rock lobster instead of tropical rock lobster.

But why should we give some varieties of seafood a tick and others the flick?

The AMCS base its decisions on the status of fish populations or 'stocks' - whether they are "faring well", "on the edge" or "overfished".

Unravelling the tangled net

But trying to unravel the status of Australian fish stocks is a tricky task.

Depending on its provenance, the fate of a species may be managed by a state or territory government, by the Commonwealth, jointly by a state and the Commonwealth, or through international arrangements.

If that's not confusing enough, there are no independent assessments of fish stocks managed by Australian states or territories. Only fisheries managed by the Commonwealth Government get an annual report card from the Bureau of Rural Sciences.

Keith Sainsbury, an internationally awarded fisheries scientist and board member of AFMA, is quick to point out that these figures actually show a remarkable improvement over the last few years and are evidence that the enormous effort invested in reducing overfishing has paid off.

There's more to the report card than the final score, though.

"Overfishing is no longer taking place on any stocks that are managed solely by the Commonwealth," says Sainsbury.

But he admits there's still overfishing of some stocks jointly managed through international agreements, including big-eye tuna, southern bluefin tuna and yellowfin tuna.

National regulations don't hold all the answers because large predatory fish such as tuna don't exactly concern themselves with borders as they chase food from Australian territory and out into the deep blue reaches of international waters, where they're subject to foreign fishing.

"We need international agreement to bring in constraints," says Sainsbury. "And other countries simply cheat on the agreements." For example, Japan has misreported figures, sometimes under reporting the catches by half, he says.

And that's why, according to the AMCS Sustainable Seafood Guide, we should "think twice" or say "no thanks" before tucking into tuna.